Since 1888 in which F. Reinitzer, an Austrian scientist, synthesized liquid crystals for the first time, the real development of the liquid crystal industry just has been nearly 30 years. The liquid crystal display (LCD) materials have obvious advantages, such as low driving voltage, small power consumption, high reliability, large information display capacity, color display, no flickering, and possibility of flat panel display, liquid crystal monomers and LCD have experienced tremendous growth. Over 10,000 kinds of liquid crystal materials have been synthesized from liquid crystal monomers, thousands of which are commonly used. According to the center bridged bond and ring characteristics of liquid crystal molecules, the liquid crystal materials are mainly classified into biphenyl liquid crystals, phenylcyclohexane liquid crystals, ester liquid crystals, alkyne liquid crystals, difluoromethoxy bridge liquid crystals, ethyl liquid crystals, heterocyclic liquid crystals, etc. The liquid crystal display also has developed from black-and-white small-screen TN and STN 30 years ago to current color large-screen TN-TFT, VA-TFT, IPS-TFT, PDLC, etc.
Novel liquid crystal display modes mainly include optically compensated bend (OCB) mode, in-plane switching (IPS) mode, vertical alignment (VA) mode, axisymmetric microstructure (ASM) mode, multi-domain twisted nematic (TN) mode, etc.
Different display modes have different liquid crystal cell designs, different driving modes, as well as different liquid crystal directors and glass substrate directions. The liquid crystal director is parallel to the glass substrate direction in case of OCB and IPS modes, and perpendicular to the glass substrate direction in case of VA and ASM modes in the absence of an electric field.
In case of homogeneous alignment IPS mode, the liquid crystal dielectric anisotropy (Δ∈) may be either positive or negative.
As for the VA mode, all liquid crystal molecules are perpendicular the glass substrate direction and parallel to the vertical incident light at zero field. Being orthogonal, the polarizers exhibit good dark state, resulting good contrast, so that the dielectric anisotropy (Δ∈) of the used liquid crystal must be negative. The liquid crystal optical anisotropy (Δn), the liquid crystal cell thickness (d), the incident light wavelength (λ) have almost no effect on the contrast. The response time of the VA mode is much shorter than that of the TN mode, approximately around half. Under the influence the applied voltage, the VA device, the OCB device and the TN device generate bend, splay and twist deformation of liquid crystal molecules, respectively, and the response times are inversely proportional to the bend, splay and twist elastic constants, respectively. For most of the liquid crystals, normally, the bend elastic constant is larger than the splay elastic constant, and the splay elastic constant is larger than the twist elastic constant, which is the reason why the VA device has shorter response time.
DE10 2002 004 228.4 and JP2005120073 disclosed the following compound:

wherein R′ and R″ represent an alkyl group. The two lateral fluorine atoms and the intramolecular rigid dibenzopyran ring restrict the deflection between the two benzene rings, such that such compounds have higher absolute values of dielectric anisotropy, and very high birefringence. However, as the consequence of the rigid dibenzopyran ring, such alkyl-substituted dibenzopyran ring liquid crystal compounds have poor miscibility, and are easy to separate out at a low temperature. In order to make the performance of the display device closer to the ideal state, researchers have been working on novel liquid crystal compounds, which moves forward the continuous development of the performance of the liquid crystal compounds and display devices.